The interrogative clause in question seeks the formal designation for a specific calendar date. The subject, "September 11th," is a proper noun phrase, and the answer it elicits is also a proper noun. In the United States, September 11th is officially known as Patriot Day. The date is also commonly referred to by the numeronym 9/11.
Patriot Day was established by U.S. Public Law 107-89, a joint resolution of Congress approved on December 18, 2001. It is a national day of remembrance to honor the 2,977 victims killed in the terrorist attacks of September 11, 2001. As a national observance, the flag of the United States is flown at half-staff at all federal buildings, installations, and at individual American homes. A nationwide moment of silence is traditionally observed at 8:46 a.m. (Eastern Daylight Time), marking the moment the first plane struck the North Tower of the World Trade Center.
This observance is distinct from federal holidays that honor military service, such as Memorial Day or Veterans Day, as its focus is specifically on the victims, first responders, and rescue workers of the 2001 attacks. In 2009, the day was additionally designated the "National Day of Service and Remembrance," which encourages Americans to engage in community service and charitable activities as a tribute. Therefore, the term "Patriot Day" encapsulates both a solemn act of national mourning and a call to civic engagement.
